Temperature responsive safety devices for munitions

Abstract

The invention comprises devices for mitigating the explosive reaction of a munition when it is subject to an external thermal hazard threat. The devices are based on the use of shape memory alloys. In one arrangement there is device which consists of a connector that is at least in part formed from a shape memory alloy, which typically undergoes large dimensional changes when heated or cooled through a particular transition temperature range. The connector in this invention is designed to form a locking engagement, between two components of a munitions casing at one temperature, but when subjected to external heating through the transition temperature range will deform to allow the connector to disengage and thus release the two joined components, allowing any build up of pressure to be released quickly. Advantageously if the co-operative parts of the connector and components are threaded portions, then the locking engagement will be capable of being dismantled during normal servicing of the munition. The co-operative parts of the connector may be integral with the components to be connected. In another arrangement the device is an annulus and is located around a munitions casing such that upon heating through its transition temperature range will cause the annulus to contract, thereby rupturing the munitions casing, allowing any build up of pressure to be released quickly.

1. A munitions casing comprising an annulus of a shape memory alloy disposed around said casing which shape memory alloy has been subjected to a combination of mechanical and thermal treatments so as to impart a memory wherein upon subsequent heating to a predetermined temperature, said memory causes said annulus to contract radially inwardly and rupture the said munitions casing. 
   
   
     2. The casing as claimed in  claim 1 , wherein the shape memory alloy is selected from Cu—Al—Zn, Cu—Al—Ni, Cu—Ni—Al—Zn—Mn, Cu—Zn—Al—Mn and Ti—Ni alloys. 
   
   
     3. The casing as claimed in  claim 1  wherein the annulus is a wire winding and is wound within a housing which is located around the casing. 
   
   
     4. The casing as claimed in  claim 3  wherein the housing extends wholly or partly around the perimeter of the monition casing. 
   
   
     5. The A casing as claimed in either  claim 3 , wherein the housing is U-shaped or rectangular in cross section. 
   
   
     6. The A casing as claimed in  claim 5 , wherein part of the length of the housing is provided with a flange which extends laterally on each side of the base of the housing. 
   
   
     7. The casing as claimed in  claim 3 , wherein the walls of the housing are cut to provide reduced flexural stiffness. 
   
   
     8. A method of using a munitions casing as clamed in  claim 1  comprising locating the annulus, around the outer surface of the munitions casing and arranging for an internal heater to be applied to said at least one annulus, wherein the internal heater is capable of providing subsequent heating to the predetermined temperature so as to cause the annulus to rupture the munitions casing. 
   
   
     9. The casing as claimed in  claim 1 , wherein the shape memory alloy has a transition temperature range which lies in the range of 80°C -150°C. 
   
   
     10. The casing as clamed in  claim 1 , wherein the annulus is comprised of a plurality of windings of shape memory alloy in wire form. 
   
   
     11. The casing as claimed in  claim 1  which is a casing for a shell, bomb, torpedo, missile or rocket motor. 
   
   
     12. The casing as claimed in  claim 11 , wherein the munitions casing is an overwound munition. 
   
   
     13. The casing as claimed in  claim 11  containing an energetic material. 
   
   
     14. The casing as claimed in  claims 13  wherein the energetic material is propellant or high explosive. 
   
   
     15. The casing as claimed in  claim 1 , which forms part of a launch tube assembly. 
   
   
     16. A method of manufacturing a munitions casing as claimed in  claim 1 , wherein the annulus of the shape memory alloy is
 i) subjected to a combination of mechanical and thermal treatments and is selected to have a composition such that, when installed around the munitions casing and subjected to subsequent heating to a predetermined temperature, said annulus will contract radially inwardly and rupture the said munitions casing; and 
 ii) installing the pretreated annulus of the shape memory alloy around the munitions casing. 
 
   
   
     17. The method of  claim 16  wherein the shape memory alloy that forms the annulus is stretched or expanded at a temperature below the predetermined temperature prior to fitting on the munitions casing. 
   
   
     18. The casing as claimed in  claim 1 , wherein the annulus is comprised of a solid ring of shape memory alloy.